Cathode for electrolytic devices



A ril 11, 1939. J. B. BRENNAN CATRQDE FOR ELECTROLYTIC DEVICES Filed Aug. 7, 1954 Snnentor 'JZJEP/ 5 Elem/WM Ella Gttomeg Patented Apr. 11,1939

UNITED STATES. PATENT OFFICE 2,154,026 CATHODE FOB ELECTROLYTIC DEVICES Joscph-BJBrennan, Fort Wayne, Ind.

Application 7,

This invention relates to electrolytic devices such as electrolytic condensers, rectiflers, lightning arresters, and similar devices. Insofar as common subject matter is concerned, this application is a continuation in part of my'prior applications Serial No. 673,772,!1led May 31, 1933,

and Serial No. 707,149, filed January 18, 1934.

Reference is hereby made to my application Serial No. 748,247, filed October 13, 1934.

In my prior applications aforesaid, I disclosed electrolytic condensers and methods of making same wherein anodes of film forming material,

such as aluminum, are employed and wherein the 1 anodes are etched by means of a solution of a salt of a metal below the film forming metal in the electrochemical series, and thereafter a dielectric fllm is formed over the roughened sur face obtained by the etching. v

In my prior specifications, it was 'stated'that go the method of treatment could be applied to cathodes as well as anodes. The present application relates particularly to cathodes for electrolytic condensers and to electrolytic condensers embodying cathodes having roughened surfaces.

It is among the objects of my invention to provide electrolytic condensers and cathodes therefor which are more durable and efliclent than present types of condensers and cathodes. An-

other object of my invention is to produce condensers having low resistance and power factor losses. Another objectof my invention is to provide acathode which will withstand corrosion even under severe operating conditions. An-

other object is to provide a condenser in which contamination of the electrolyte by reason of corrosion of the cathode is substantially prevented.

Further advantages and objects of my invention will become apparent from the following 6 description of a preferred form thereof, reference being made to the accompanying drawing which shows a cross section of .a well known type of condenser embodying my invention.

In the production and use of electrolytic con- 5 densers of the type having anodes with dielectric films formed t great deal of di culty has been.encountered because of the corrosion of the cathode. I have found that by etching the surface of the cathode so or otherwise treating it to produce a microscopically roughened surface, the corrosion of the cathode can be largely eliminated and at the same time the efflciency of the condenser is considerably increased. Apparently, this advantageous result is due to the fact that the actual area reon and unfilmed cathodes, a

1934, Serial No. 738,804

of the cathode in contact with the electrolyte is greatly increased with respect to the plane area thereof. This increase in area apparently results in a reduction in'the current density at the surface of the cathode, which in turn reduces the corrosion and the resistance to the flow of electric current between the electrolyte and the cathode, producing a more durable and a more eflicient ,condenser which remains cooler than prior types of condensers of similar capacity when in use.

As shown in the drawing, my condenser may comprises a substantially cylindrical container ill of aluminum, copper or other suitable metal which retains the electrolyte and which comprises the cathode of the condenser. The lower end of the container may be provided with a hollow threaded projection H for supporting the condenser in use and for forming an electrical contact for the cathode. The anode i2 is immersed within the electrolyte and may preferably comprise a sheet of aluminum foil, in cylindrical or spiral form if desired. The anode terminal comprises a supporting strip 13 which extends through the hollow projection ll, 1eak-' age of the electrolyte between the terminal l3 and the projection being prevented by means of a rubber member M. The upper end of the cylindrical container is provided with a cover I5 which may have a vent of any suitable form as indicated at it. h

In this type of condenser, the aluminum anode i2 is provided with a dielectric film which may be formed by any well known method, and preferably the surface of the aluminum is treated as described and claimed in my prior applications by etching in a metallic salt solution before the 'dielectric film is formed thereon. The etching operation produces a roughened surface on the anode and the subsequently formed dielectric film conforms substantially to the configuration of the roughened surface so that the area of the film, and correspondingly the capacity of the condenser, are both greatly increased as compared with a condenser embodying an anode of similar size which has not been so treated. The production of the anode is described in detail in my prior applications, and will not be referred to further herein.

As stated above, in my condenser I also roughen the interior surface I! of the cathode Ill in order to increase its effective area and thereby apparently reduce the current density at the surface of the cathode, and thus produce a more durable and eiflcient condenser. The container or cathode Ill is preferably formed of aluminum,

and in the case of aluminum I have obtained excellent results by the following series of steps.

The fabricated cathode before the anode and cover have been secured thereto is first washed in a five per cent solution of borax to remove grease and other surface impurities therefrom. It is essential that the surface of the aluminum be clean in order to obtain uniform results from the etching. Thereafter the aluminum may be etched with a solution of the following composition:

Water cubic centimeters 80.5 Hydrochloric acid do 8.9 Nickel chloride "grams" 22 The aluminum is immersed in the above solution for a period of from one to two minutes, although a longer or shorter period may be employed depending upon the depth of the etch desired. Then the cathode is removed from the solution and rinsed sfibcessively in cold distilled water, a twenty per cent solution of nitric acid, cold distilled water, a two per cent solution of alkali such as sodium hydroxidqand finally rinsed in boiling distilled water. The nitric acid functions to stop the etching operation whilethe last immersion in the alkaline solution assists in removing all traces of nitric acid from the surface of the cathode. The boiling water removes the alkali and any remaining traces of impurities, leaving a clean etched surface. The treatment obviously needs only to be applied to the interior surface of the container, although the entire container may be immersed in the various solutions if it is more convenient to do so.

After the cathode has been treated as outlined above, the assembling operations may be carried on in the usual manner. For example, the anode which already has a dielectric film formed thereon may be secured within the prepared cathode, then the cathode is filled with an electrolyte such as a solution of borax and boric'acid, and the cap l5 spun onto the cathode ID. The condenser is then ready for the customary further forming operations and for tests.

I have found the above outlined procedure to. be especially advantageous in connection with aluminum cathodes, although I may use other solutions such as, for example, the solutions of copper chloride, iron chloride or manganese sulphate disclosed in my application Serial No. 707,149. When other materials are used for the cathode, various other etching solutions which are well known in the art may be advantageously employed. Furthermore, if desired, the roughened cathode surface may be produced by sand blasting, scratch brushing, or by spraying molten metal thereon as disclosed in my application Serial No. 662,107-fi1ed March 22, 1933 now Patent No. 2,104,018. Obviously, my cathodes may be employed with other types of condensers, such as those embodying dry or paste electrolytes, instead of the liquid electrolyte described herein.

In this type of condenser, I preferably employ an anode having a roughened surface, although various other types of anodes will give satisfactory reults. My cathodes are particularly advantageous when used in conjunction with anodes having a high capacity per unit of plane area. Such anodes may be very small for a given capacity as compared with prior practice, and my construction makes it possible to employ correspondingly small cathodes while at the same timethe resistance and power factor losses and the corrosion of the cathode are reduced. While I have not been accurately to measure the increase in eflecti' "rea of my cathodes, I prefer to treat my ano d cathodes by similar methods, or methods which are equivalent so far as increase in area is concerned and to so proportion the plane or directly measurable area of anode and cathode so that the effective area of the cathode approximates the effective area of the anode. The proper area can be readily determined by forming a dielectric film on a sample cathode and measuring its capacity per unit of plane area when used as an anode under the conditions for which the condenser is designed. If the cathode is designed so that its capacity if provided with a dielectric film would be the same as the capacity of the anode, the effective areas of the anode and cathode will be substantially equal, for under a given set of conditions, the capacity of an electrolytic condenser varies approximately directly with the area of the dielectrio film, which in turn varies with the effective area of the electrode in contact with the electroyte.

I have found that condensers made according to my invention can be manufactured economically and that my condensers are extremely durable and free from failure, probably because the electrolyte is not contaminated by the corrosion of the cathode, as is the case with many prior types of condensers. My condensers do not over .1831, in service, have low power factor and resists nee losses, and are efficient and reliable, In particular, my condensers and cathodes have the ability to withstand for long periods of time the destructive effects of a. high alternating current ripple in the line to which the condenser is connected without over heating or failure.

Various changes and modifications in my invention will be apparent to those skilled in the art. It is therefore to be understood that my patent is not limited to the specific embodiment disclosed in this specification or in any manner other than by the scope of the appended claims when given the range of equivalents to which my patent may be entitled.

I claim:

1. In an electrolytic condenser, the combination of an anode having a dielectric film electroformed thereon and an unfllmed cathode having a microscopically roughened surface.

2. An aluminum cathode for electrolytic condensers of the type embodying an anode having a dielectric film thereon, said cathode comprising a container for the electrolyte having an etched interior surface whereby the area of the cathode directly in contact with the electrolyte is greatly increased.

3. In an electrolytic condenser, the combination of an electrolyte, a pair of spaced electrodes immersed therein having roughened surfaces, and an electrolytically formed dielectric film overlying the roughened surface of one of said electrodes, the surface of the other of said electrodes being directly in contact with the electrolyte.

4. A cathode for electrolytic condensers of the type having electrolytes, said cathode having a roughened surface adapted to be directly in contact with the electrolyte of the condenser.

5. A cathode for electrolytic condensers of the type having electrolytes, said cathode having an etched roughened surface adapted to be directly in contact with the electrolyte of the condenser.

6. An electrolytic condenser comprising an electrolyte, an anode immersed therein, and a cathode of film forming metal adapted to contain the electrolyte, said anode having a roughened surface having an electro-formed dielectric film overlying said roughened surface, and'said cathode having a roughened surface, the effective area of said cathodesurface being at least substantially as large as the effective area of said anode surface.

7. An electrolytic condenser comprising an electrolyte, an anode immersed therein, and a cathode adapted to contain the electrolyte, said anode having an electro-formed dielectric film in contact with the electrolyte, and said cathode having roughened surface directly in contact with the electrolyte, the effective area of said cathode surface in contact with the electrolyte being at least substantially as large as the effective area of said anode surface.

8. An electrolytic condenser comprising an electrolyte, an anode having a roughened surface and a dielectric film overlying said surface and in contact with said electrolyte, and a cathode of film forming metal having an etched surface directly in contact with said electrolyte.

9. An electrolytic condenser comprising an electrolyte, an anode immersed therein, an electrc-formed dielectric film overlying the surface of the anode, said film being in contact with said electrolyte, and a cathode of film forming metal roughened cathode surface in contact with the electrolyte being at least substantially as great as the effective area of the filmed anode in contact with the electrolyte.

11. The method of preventing the corrosion of cathodes of electrolytic condensers of the type embodying the film forming electrolyte and an anode having a dielectric film thereon which comprises roughening the surface of thecathode in contact with the electrolyte to thereby increase the effective surface area of the cathode.

12. An aluminum cathode for electrolytic condensers having an electrolyte, said cathode having an etched surface adapted to be directly in contact with the electrolyte of the condenser.

' JOSEPH B. BRENNAN. 

